In a 4-wheel drive vehicle (4WD vehicle), a rear-wheel drive vehicle (FR vehicle), and the like, a propeller shaft is used for transmitting a rotational drive force from a transmission to a differential. In such a propeller shaft, at the time of vehicle crash, the propeller shaft stiffens, to thereby increase an impact force generated on a vehicle. Thus, a pipe part coupled to a constant velocity universal joint is bent in a laterally-laid V-shape so that the bent part sometimes intrudes into a vehicle interior.
Accordingly, there are conventionally proposed various mechanisms for absorbing axial displacement generated at the time of crash (Patent Literature 1 to Patent Literature 3).
As disclosed in Patent Literature 1, the tubular shaft is coupled to the outer joint member of the constant velocity universal joint, and at the time of impact, the inner-joint-member peripheral unit (interior parts) of the constant velocity universal joint (such as the stub shaft, the inner joint member, the balls, and the cage) can push the sealing plate aside to thrust into the hollow portion of the tubular shaft. As disclosed in Patent Literature 2, the tubular shaft is coupled to the outer joint member of the constant velocity universal joint, and at the time of impact, the shaft can break through the sealing plate to thrust into the hollow portion of the tubular shaft. As disclosed in Patent Literature 3, at the time of impact, the inner joint member of the constant velocity universal joint can push the sealing plate aside to thrust into the hollow portion of the tubular shaft.
By the way, Patent Literatures above each disclose a plunging type constant velocity universal joint allowing axial displacement as the constant velocity universal joint. However, a fixed type constant velocity universal joint illustrated in FIG. 23 is also used for the propeller shaft.
The fixed type constant velocity universal joint illustrated in FIG. 23 comprises: an outer joint member 3 having an inner spherical surface 1 in which a plurality of track grooves 2 are formed equiangularly along an axial direction; an inner joint member 6 having an outer spherical surface 4 in which a plurality of track grooves 5 paired with the track grooves 2 of the outer joint member 3 are formed equiangularly along the axial direction; a plurality of balls 7 interposed between the track grooves 2 of the outer joint member 3 and the track grooves 5 of the inner joint member 6, for transmitting torque; and a cage 8 interposed between the inner spherical surface 1 of the outer joint member 3 and the outer spherical surface 4 of the inner joint member 6, for retaining the balls 7. In the cage 8, a plurality of pockets 9 for receiving the balls 7 therein are provided along a peripheral direction.
A female spline 10 is formed in an inner surface of a hole portion of the inner joint member 6. Into the hole portion of the inner joint member 6, a male spline 12 of a shaft 11 is fitted, and thus the male spline 12 is fitted to the female spline 10 of the inner joint member 6. Further, to an end portion of the male spline 12, a snap ring 13 for preventing slipping-off is fitted.
In order to seal opening portions of the outer joint member 3, an end cap 15 and a flexible boot 16 are mounted thereto. The flexible boot 16 comprises a bellows 18 made of a rubber material or a resin material, and a cylindrical adapter 19 made of a metal. The bellows 18 comprises a small-diameter end portion 18a outwardly fitted to the shaft 11, a large-diameter end portion 18b connected to the adapter 19, and a bent portion 18c provided between the small-diameter end portion 18a and the large-diameter end portion 18b. The small-diameter end portion 18a of the bellows 18 is fastened by a band 20 and thus fixed to the shaft 11. The adapter 19 comprises a caulked portion 19a caulked and fixed to the large-diameter end portion 18b of the bellows 18, and an annular flange portion 19b fitted to the outer joint member 3. Note that, the end cap 15 comprises a body portion 15a shaped into a bottomed short cylinder, and an annular flange portion 15b fitted to the outer joint member 3.
A curvature center O2 of the track groove 5 of the inner joint member 6 is displaced from a joint center O to the end cap side in the axial direction. A curvature center O1 of the track groove 2 of the outer joint member 3 is displaced from the joint center O to the flexible boot side in the axial direction. That is, the curvature center O2 of the track groove 5 of the inner joint member 6 and the curvature center O1 of the track groove 2 of the outer joint member 3 are offset with respect to the joint center O by equal distances F, F in axially opposite directions.
As illustrated in FIG. 24, a companion flange 41 is mounted to the outer joint member 3. The companion flange 41 comprises: a base 41a mounted to the opening portion of the outer joint member 3 situated on a side opposite to the adapter 19; and a cylinder body 41b provided continuously to the base 41a. The base 41a comprises a thick portion 42 and a thin portion 43, and the end cap 15 is inwardly fitted to the thick portion 42.